Radio frequency communication system



Jan. 29, 19.

L. BE'GIN RADIOFREQUENCY COMMUNICATION SYSTEM -2 Sheets-Sheet FiledMarch 1926 avwemtoz LU CIEN BEGlN g l qhisr aflomm 'ai g I Jan. 29;1929. I 1,700,580

L. BEGIN RADIOFREQUENCY COMMUNICATION SYSTEM Filed March 1926 2Sheets-Sheet 2 22 \l qr 11k 4,

Him I mmma gvwemtoz LU CHEN BEGN 1" "W I a UM Patented Jan. 29, 1929 IUNITED STATES.

- 1,700,580 PATENT OFFICE.

LUCIEN BEGIN, or rears, raANonnssIeNon or ONE-HALF 'ro WILLIAM B.WEAVER, or BIRMINGHAM, ALABAMA, AND HAROLD r, WILHELM, on NEW YORK, N.Y.

:aAnIornnoUENoY oommu'NIcA'rIoN SYSTEM.

Application filed March 2, 1928, Serial No. 91,669, and in France March13,1925.

particular, insignalling networks comprisin a plurality ofcorrespondents making use 0 'but a limited number of signallingfrequencies.

It is known that there exist duplex signalling networks comprising aplurality of correspondents which, just as in shipboard and coastalstations, make-use of but one and the same stand-by wave-length and inwhich the calls are discriminated by the manual or {5 automatictransmission of a given number of wave trains for each station, theseimpulses being selectively translated at the called station either intoa single signal by means of mechanical selector mechanism or by the Imere acoustic identification of a predetermined series of impulses. Onthe other hand, it

it is possible to establish a two-way communication between two stationssuch as M, N,

2 providing'reception at each station be made to take place at a wavefrlaquenc sufficiently different from that used therein or transmission,which amounts 'to. say that station M -mus t transmit waves of sayfrequency f and receive on frequenc f WhllShStltlOIl N must do theopposite. hen it is desired to extend this classical method of duplexsignalling to f f a network comprising a plurality of correspondentssuch as M, N, O, P, it is obvious is also known that two othercorrespondents without the. latter perceiving his interferingcarrier-wave.

In accordance with one application of the present invention, thepossibility of such disturbing carrier wave transmission by thirdparties is eliminated while yet allowing the third party to listen in.-This is accom' lished by first selectively calling-the desire party onlyand then by locking the 'transmittin equipment of all the other.stations comprised in the network. With this object in view, a

given party shall be called by transmitting waves of the same frequencyas that to which the stand-byapparatus of all the stations is tuned, andthen by modulating those waves at a relativelylow frequency, --disti nctfor each statiomaswell as by designing the'if stand-by equipment of eachstation such as wave frequencies 'for' duplex communication between anytwo stations, Fig. 2 illustrates another mode of carrying out theinvention by the use of electron dis- I charge tubes.

Referring now to 1, in this'figure the terminals of the apparatus,leading to either munication or to the line conductorsin the case ofwired commumcation, are denoted the serial system in the case ofwireless comby 60. Those terminals lead, on the other hand, to twocoupling systems 48-- 50 51 -53 and 48-50-51-52 one of which is providedto transmit efiiciently a given, frequency, such as f, to the exclusionof all other frequencies'and particularly of frequency f whilst theother system is provided Q P to. do the opposite. Assume the arrangementdesignated by48-'50-51- 53 is provided to efiicientlytransmit f and thearrangementdes'ignated by 48-50-51-52 is provided to transmit f. In thatcase, trans- 5 that the operation, at any given moment,

. must be restricted to the communication be-' I ,t'ween anytwo stationswith the momentary exclu'sion of all the other stations, just as inparty lines comprising several subscribers 5 sets. In the latter case,however, it is usually;

" possible for any subscriber whatever, other v than the two alreadycommunicating, to he ten in towhat is going on over the line without theknowledge of the two active corre 45 'spondents. In carrier wave duplexsignaL, ling, however, the apparatus is usually so designed thatit'suflic'es to liftthe receiver of thehookfso that the transmittinggear be automatically thrown into operat ve condi- 5 .tion and thecarrier wave itself emitted even if. the operator does not modulate itsampliq tude by speaking in front of the microphone. It is obviousthat,-under such conditions, it I is hardly possible for a third party.to listen as in to the communication taking place between former-48should not permit the .transmission of f and, reciprocally, it shouldnot be j possible to transmit frequency f through transformer 48. Withthat object in view,

one of 'thewindings of 48=shall be shunted by a parallel circuit- 5Otuned to f and having a-high C/L ratio so as to offer. but negligible*reactance for short-circuiting all fr other then f and then there shallbe inserted waves of frequency), i. e., all frequencies excepting 'fwill be highly shunted by the trap circuit 51 and then frequency f inparticular will be highly impeded by the series rejector 50 tuned tothat frequency. By means of the relays 54, 55, each acting as a doublepole double-throw switch, it will be possible to assign either of thesecoupling vunits to the detector 56 and the other to the transmitter 31,or conversely.

During the stand-by period, the output of detector 56 is connected tothe exciting winding of a relay 40 through the primary of transformer 14having a trap circuit 13 across its terminals and serially through theback contacts of three other relays 41, 47

and 43. Relay 40 is shunted by a condenser cuit of battery 22 throughcontacts 59 and the Winding of a drop relay 20, the latter being shuntedby a condenser 19 which by passes the undulatory component of thecurrent. The parallel circuit 13 is tuned to the each station, and itsobject is to provide a shunt of negligible reactance to all modulationfrequencies other than that intended to' operate the fork relay 57 ofthe called station.

Terminals 33 of the transmitter 31 are intended to be connected to themodulating system, that is, to the keying arrangement in the case oftelegraphic signalling and to the microphone system in the case oftelephonic signalling, and, during the calling period only, to a sourceof definite low frequency,

distinct for each station to be called.

In the drawing the telephone transmitter 24 may be connected. thrutransformer 25 and filter 26 to the. back contacts of relay 30.

'The front contacts of relay 30 may be conne'cted selectively to eithersource of low frequency 28 or 29 depending on the position of key 27Relay 30 may e operatedby.

depressing key 37. The low or modulating frequency source 28 or 29 maybe' connected according to which station it is desired to call. Thearmatures of relay-30 may be connected to terminals 33 of thetransmitter 31 to. modulate the high frequency output of current.

While transformer 14 at each station will be designed so as toefliciently transform only waves of the frequency of fork 57 to which itis connected, and which corresponds to the modulation frequency forcalling that station, it will be advisable, however, to avoid the forkrelays of the uncalled stations being put into operation b successivetransient resonance effects resu ting from those components df speechmodulation as may coincide with the natural time period of'the variousforks. With that end in view, forks having natural time periods aswidely separated as possible from the focus of the speech frequency sectrum shall be chosen and then a suitable lter circuit 26 shall be usedto sup-- press right at their origin, i.e., in the microphone system,such components of the speech transmitter 31 with the desired modulatingas coincide with the modulation frequencies frequencies exclusively soas not to distort the speech by excessive curtailment of thosecomponents which determine its intelligibility.

Let us now consider a few possible conditions of operation of thesystem, when the detector 56 1s connected say to the couplingarrangement for f, as illustrated. (a)-One of' the distant stations ofthe network transmits an unmodulated carrier wave of frequency f, whichmay be the standby frequency. Under those conditions there will appearat terminals 60 from the distant station a corresponding alternating E.M. F.,

which will be transmitted'to the input ter-- minals of 56 through theselective couplernatural-time period of the fork relay 57 at- 4850-5l*53 which, will give rise, in

the output circuit of 56, to a direct current of constant mean value.This constantcurrent will operate the relay 40 through'the primarysystem of 14 and the back contacts of relays 41, 47 and 43. It isobvious that this direct current flowing the primary system of 14 willbe without effect on its-secondary. The v closing of bu'sy'relay 40will, on one hand operate the busy signal 38 and, on the other.

hand, will-prevent all possible operation of transmitter starting relay41 through the receiver being eventually lifted off the hook 42.

(b)-One of the stations transmits a carrier-wave of frequency f also butmodulated at a frequency other than that of the fork 57 at the stationconsidered. The effect of this transmission on the standby apparatus ofthe receiver in question will obviously be the 6 in to a conversationoffering eneral interest in the operation of the networ A monitoringrelay 47, operated by a push-button 46 on the desk set, has thereforebeen provided in I orderto enable him to connect his receiver 11 withthe output of detector 56 through trans-.

former 12, by substituting"- the primary of the latter for the stand-byrelay 40, transformer 14" and trap 13, by means of one of the makecontacts of relay 47 without,-however, un-

15 looking his transmittervstarting equipment.

(0)- One of the stations transmits a carrier wave of frequency fmodulated at the natural frequency of trap circuit 13 and hence at thatof fork 57. Under those conditions,

there will be'obtained, at the output of detector 56, a unidirectionalcurrent the mean amplitude of which will vary at the frequency of trapcircuit 13. The latter will then behave as a very high impedance for thelow frequency component and will hence give rise to a large potentialdrop across its terminals. The primary winding of 14 will therefore besubjected to an alternating E. M. F. corresponding to that of themodulation of the calling carrier wave.- This E. M. F. will betransferred across the secondary which will in turn operate the winding58 setting 57 into vibration. I 1

As stated above, the vibration of fork 57 will cause the operation ofthe droprelay 20.

The drop will in turn operate the ringing relay 43, the operation ofwhich will, on one 'hand result in the closing of the circuit of bell 45and call 1amp44, and, on the other I 40 hand connect the telephonetransformer 12 to the output of detector 56 in place and instead I of 14and 40. The switching out of the latter will prevent sustained operationof the .busylamp 38 and locking of starting relay 5 41. The operator atthecalled station considered may therefore lift the receiver oif 42 aand thereby close the starting relay 41 which I will in turn make acontact at the starting terminals 34 of the transmitter through one Q ofthe back contacts of monitoring relay 47 and battery 22, on one hand,and, on the other hand willcause the bell to cease operating by openingits circuit. I

It will be understood that by placing battery 22 on the startingterminals 34, the trans-' mitter 31 whichmay be an electron-dischargetube will be started. If there be any modujlating potential at theterminals 33, the high frequency current generated by the transmitterwill be modulated thereby.

The communication will thus be established between the called stationand the stat on having transmitted the call. On replacing the receiverat 42 at the end of the communication, call lamp 44 and bell 45 willgive the which would correspond to a call initiated by ometer slider andthe ositive terminal of hatthrough signal informing the operator that hemust lift the drop of relay 20 and thereby restore the stand-byconnections. I It will be noted that the exciting windings of shift-overrelays 54, 55, are connected in parallel with startin terminals..34'ofthe transmitter 31 throug one of the back contacts'of ringing relay 43.They will therefore be operated simultaneously with the startingequipment branched at 34 providing, however, that ringing relay 43 hasnot been operated just previously to the receiver be- I ing'lifted oilthe hook. Incase ringing relay 43 would not have operated previously,

the local station, the shift-over relays 54, 55, would then be operatedsimultaneously with the starting equi ment connected at 34 andtransmission Wou d then take place" on frequency f whilst receivingwould automatically be carried out on frequency f. I It will be.understood that transmitter 31 gen erates both frequencies f and ffrequency v f being transmitted and f being suppressed, if thearrangement 485051 53 'be' con- 9 nected to the transmitter; andfrequency f being transmitted. and f being suppressed, if thearrangement 485051'-52 be connected to the transmitter. There will'thusbe realized a duplex signalling system in which transmission willautomatically take place on f and reception on f if it is-the stationconsidered which initiates a call, but in which the opposite willautomatically occur if the station'set's his apparatus into operation asa result of a received call. Referring now to Fig. 2, there is shown adiagrammatic representation of another mode of carrying out theinvention which comprises the use'of a three-electrode tube detector forrectifyin the carrier wave in place and instead of t e schematicdetector 56 of Figure -1' and also of a second threeelectrodetube 16 forrectifying the low-fie quenc alternating component of the calling moduation. Tubes 3 and 16 have their filaments heated by the common source 7through steadying or ballast resistors 5 and 18, voltmeters 4 and 17being branched across their respective filament terminals in order tothrough the carrier-wave input circuit 1-2 and the in ut circuit14-15 ofthe low-frequency ca ling device. Potentiometer '9 is branched across abattery 6 intended to suitably bias the grids with negative potential. ICapacity 10, branched across the potenti tery'. 6 operates in y-passinoscillations around the potentiometer resistance, The output circuits ofboth tubes are also fed off I a common source 8. I The output circuit oftube 3 is connected to the various elements ofthereceivingapparatus in amanner simi larto that of. the detector 56 of Figure 1.

One oft-he mainadvantages of the diagram. of Figure 2. is that itenables the use ofliiglier'modulation frequencies for effectwhich areuseful in maintaining the natural characteristics ofthe speaker. On theother hand, inthose stations provided with but low' transmitting power.and making use of high- 1y resonant circuits, care will have to beexercised not to modulate .the callingpcarrier wave at an excessivefrequency for it can be shown that. the same would involve a decrease intransmission. efliciency resulting fromthe virtualuntuning of thecircuits due to modulation. 'In fact, a carrier wave of frequency fmodulated at a lower frequency F gives rise to waves of: frequenciesfl-F", f and f -l-F It willthus be seen that a ortion of' the totalpower of the unmoduated wave will appear in the form of waves of dierent' frequencies which, in view of the highly resonantcircuitsused,will not befiansmitted as efficiently as'the wave f itse In thisfigurethere is. shown a push-button 37 used ior. the operation of relay 30through battery 22.. The operation of this relay re-- sults in thesubstitution, during the calling period, of one of the low-frequencysources 28, 29, to the microphonesystem 2425-26, normally branched.across modulation terminals 33 of'the transmitter 31. F

In the case of a network wherein communications between various stationsare not very frequent, it will be possibleto effect an economy byswitching. the second tube 16 out of circuit during the stand-byperiodproviding,

1 howeventhat it be automatically re-insertedinthe circuit as soon as.a. call is despatched by any other station ofthe network. Figure 2 showsa diagrammatical form of realizing this disposition. It will suffice toopen the switch 23 normally closing the filament circuit-oftube 16* andthen to utilize, in parallel with 23, one of the make contacts of relay40in order'to restore theclosing of same followingthe arrival ofanycarrier-Wave.

The output terminals 32 of thetransmitter are' branched to an outputcoupler-36-35E which may lead to an antenna, a loop, or a line circuitin accordance with known methods.

The low-frequency sources 28, 29, for mod ulating the calling carrierwave may be. constituted. by ordinary'microphone hummers or wtuningiorkoscillators operating in front of the. microphone, providingthe filter 26 be simultaneously put out of circuit, or else by utilizingone of: the. amplifying or modulatingtubes as alow frequency osclllatorduring the calling period. In the. latter case, it will be. preferableto make. use ofcircuits compris ing no magnetic coredinductancesin.order to avoid that: the fundamentalifrequencies thereby obtained forcalling modulation be not accompanied by harmonics which might. op-

erate. the fork relays of other stations. than the one called by agiven, fundamental.

It: goes without saying that the-vibrating Y relay has. been representedschematically by a tuning fork relay 57 and that, in accordance with theinvention, thesame' maybe replaced by any equivalent vibrating relay,suchv as vibrating reed relays etc. This remark also holds good asregards. the other switching relays represented onl in their schematicform. In particular, the rop relay 20 may be replaced by a polar relaythe armature. of which will be deviated in one direction by the volt-.age appearing across the b -passing condenser 19 and thereby establishcontact 21, and which will be deviated in theo posite ii-- rection by anopposite voltage res ting from the through signal and therebyrestore thestand-by connections. In a siimlair manner, the coupling units 48-50--51'-53 and 4850--51-52 of Figure 1 may be replaced by theelementary couplers of Figure2. Different batteries 22 have been shownin order to simplify the diagram of connections, but it must beunderstood that thesebatteries may merge into a single commonbattery' inaccordance with well-known. common battery practice. Lastl it will bepossible to insert amplifiers fore. andfollowin either for both tubesv 3and 16 aswell; as be ore and following the schematic detector 56.

Having thus described the invention, I claim:

-' 1-. In a. high frequency communicationsys stations each having atransmitter and a receiver, means whereby any station may directlyselectively 0811 5 desired Station only 1 5' and means whereby thetransmitters of the undesiredstations are locked when said desiredstation is called.

3'. Ina high frequency communicationsys I tem, a plurality ofsignallingstations each I havmg a transmitter and a receiver, each station havinga common stand-by high'frequency and a distinctive stand-by frequency,means whereby the transmitter of any station may send out the stand-byhigh frequency and the distinctive stand-by frequency.

of the desired station, the stand-by high frequency locking thetransmitters of the undeslred stations and the distinctive stand-byfrequency causing a signal at the desired station.

4. In a communication system, a transmitter, a receiver, a coupling-unitpassing only a given first frequency, a second coupling unit passingonly a given second frequency, shift-over relays, a signalling device,starting equipment for said transmitter, said re lays normally andsimultaneously connecting the first coupling unit to said transmitterand the second coupling unit to said receiver, and means whereby saidstarting equipment may start said transmitter and shiftsaid relays tointerchange the connections of said coupling units with said transmitterand receiver if said signalling device has not been operated justpreviously to said starting equipment and yet only start saidtransmitter if said signalling device has been operated just previousiy1to said starting equipment.

a communication system, a transmitter, a receiver, a coupling unitpassing only a given first frequency, a second coupling unit passingonly a given second frequency, and means for simu taneously assigningany one of said coupling units to said transmitter and the other of saidcoupling units to said receiver, selectively,

6. In 9. hi h frequency communication sys tem, asi'gna ing stationcomprising, distinctive signalling apparatus responsive to a distinctivesignal, a busy relay, a receiver, a receiver hook, a detector, atransmitter, a

" ringing relay responsive to o eration of said apparatus to give signalan to de-energize said busy relay, a transmitter starting relay underseries control of said hook and said busy relay, said transmitterstarting relay 7 being operated by said hook to place said receiver incommunication with the detector tem, a signallin station comprising areceiver, atransmitter, distinctive signalling apparatus responsive to adistinctive signal, a. busy relay, a transmitter starting relay, areceiver hook, a detector having one output terminal connected thru saidapparatus and busy relay to a back contact of said transmitter startingrelay, said terminal also being connected thru said receiver to theforward contact of said transmitter starting relay, the armature of saidbusy relay being in series with said hook and said transmitter startingrelay, the other output terminal of said detector being connected to thearmature of said transmitter starting relay.

8. In a high frequency communication system, an electron discharge tubedetector having a trap circuit tuned to a distinctive fre-- quency and abusy relay in its anode circuit, a rectifier circuit connected acrosssaid trap circuit and comprising a second electron dis charge tube, thecathode heating circuit of said second tube having in its path anarmature of said busy relay, said armature being normally open, saidbusy relay causing said second tube to function and operating a busysignal when a stand-by frequency isimpressed on said detector.

9. In a high frequency communication system, a detector having an outputcircuit which includes a trap circuit, a rectifier circuit connectedacross said trap circuit and including an electron discharge tube, andmeans in said outputcircuit for controlling the cathode heating currentof said tube.

10. A high frequency communicating system comprising at least twostations each having a transmitter and a receiver, said stations havinga common stand-by frequency, said having means for receiving said fruencies only means whereby any station, if initiating a ca must transmiton the stand-by frequency only and receive on the second freqency only,and, if receiving a call, must recome on thestand-by frequency only andtransmit on the second frequency only.

' ".LUQIEN BEGIN.

